首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   172350篇
  免费   16347篇
  国内免费   9225篇
电工技术   13778篇
技术理论   8篇
综合类   17794篇
化学工业   16905篇
金属工艺   7093篇
机械仪表   15749篇
建筑科学   20257篇
矿业工程   6641篇
能源动力   7737篇
轻工业   12716篇
水利工程   7438篇
石油天然气   8229篇
武器工业   2000篇
无线电   9826篇
一般工业技术   16490篇
冶金工业   6650篇
原子能技术   2519篇
自动化技术   26092篇
  2024年   368篇
  2023年   1952篇
  2022年   3893篇
  2021年   5001篇
  2020年   5115篇
  2019年   4329篇
  2018年   4196篇
  2017年   5206篇
  2016年   6345篇
  2015年   6742篇
  2014年   11073篇
  2013年   11123篇
  2012年   12969篇
  2011年   14326篇
  2010年   10261篇
  2009年   10483篇
  2008年   9839篇
  2007年   11785篇
  2006年   10228篇
  2005年   8605篇
  2004年   7274篇
  2003年   6213篇
  2002年   5019篇
  2001年   4123篇
  2000年   3527篇
  1999年   2938篇
  1998年   2527篇
  1997年   2124篇
  1996年   1670篇
  1995年   1434篇
  1994年   1286篇
  1993年   960篇
  1992年   889篇
  1991年   648篇
  1990年   543篇
  1989年   468篇
  1988年   389篇
  1987年   265篇
  1986年   229篇
  1985年   218篇
  1984年   253篇
  1983年   240篇
  1982年   199篇
  1981年   97篇
  1980年   94篇
  1979年   65篇
  1978年   54篇
  1977年   46篇
  1976年   43篇
  1959年   30篇
排序方式: 共有10000条查询结果,搜索用时 196 毫秒
991.
A model warehouse with carefully regulated environmental conditions was used to study the behavior of adult Indian meal moths during commodity infestation. Sequences of moth distributions in the warehouse, calculated by spatial analysis, clearly showed the coordinated movements of moth populations from eclosion to death. Many facets of adult behavior in a warehouse were coordinated with the photoperiod. Adult moths emerged at the end of a photophase and fairly rapidly moved to the walls and, to a lesser extent, to the undersides of the commodity pallets. Most females are mated in the first 24 h after emergence, largely during the scotophase. Air circulation within the warehouse probably compromised pheromone-directed guidance of males to females, although pheromones may still have a major role in regulating other aspects of male mating behavior. When mating subsided, many of the males flew upwind to the air circulating unit, but only during the photophases. The females moved to the return air side of the warehouse and then migrated towards the same end as the males, but only during the scotophases. They moved from pallet to pallet largely by walking on the warehouse floor and laid eggs in or on the cups of commodity. Direct oviposition on the commodity during the infestation period was lower than expected, probably because commodity odors were dissipated by air circulation and did not provide appropriate orientation. At 144 h after emergence, 90% of the moth population had died.  相似文献   
992.
刘康莲 《贵州化工》2008,33(1):25-26,30
以三聚磷酸钠生产过程为例,论述了在以纯碱为原料的非强酸性水溶液体系中,由于反应不完全导致反应物中存在少量的碳酸盐,这部分碳酸盐干扰了用酸碱滴定法测量的中和度,并据此提出中和度分析改进方法.由此可以推广到其它以纯碱为原料的非强酸性水溶液体系中.  相似文献   
993.
通过总结大关山矿硐室爆破的主要特点,并就硐室爆破实施过程中采取的新措施、新办法进行了分析。  相似文献   
994.
牙哈采油树腐蚀检查分析及对策   总被引:1,自引:1,他引:0  
介绍塔里木牙哈凝析气田高温高压井口采油树腐蚀的现象,腐蚀机理及采取的措施,对其他油田采油树腐蚀的防治起到指导借鉴作用。  相似文献   
995.
ABSTRACT: The effects of several processing factors (storage time, time in the open air at room temperature, and overhead concentrations of O2 and CO2) on color, firmness, polyphenol oxidase (PPO) activity, and sensory attributes of pears (cv. Rocha) grown in 2 locations were studied using a multiple linear regression model. Backward elimination (F ≥ 0.005) was used to assess the significant factors. Extended storage time, long‐time exposure at room temperature, and high O2 concentration played major roles on color changes assessed instrumentally and further confirmed by a sensory panel. Firmness was strongly affected by storage time and by time in the open air at room temperature. Finally, PPO activity was dependent on the growing location.  相似文献   
996.
A latent profile analysis was conducted on the co-occurring symptoms of 423 adolescents diagnosed with major depressive disorder as part of the Treatment for Adolescents with Depression Study (TADS), a multisite, randomized treatment trial. The participants had a mean (SD) age of 14.6 (1.5) years; of the sample, 45.6% was male and 73.8% was white. Scores on the primary subscales of Conners' Parent Rating Scale-Revised were used as indicators in the analysis. Five classes of symptoms best described the clinical presentation of adolescents enrolled in the TADS. Of the adolescents in the sample, 80% were assigned to classes with clinically significant elevations on 1 or more subscales of the Children's Depression Rating Scale-Revised. The 5 classes met empirical criteria for distinctiveness and were validated against clinical diagnoses, child-rated symptoms, and clinician-rated functional impairment. The findings are consistent with prior studies that showed a high rate of co-occurring symptoms among depressed adolescents. The discussion focuses on understanding subtypes and comorbidity in adolescent depression as well as the implications for treatment and for prevention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
997.
In many data analysis problems, it is useful to consider the data as generated from a set of unknown (latent) generators or sources. The observations we make of a system are then taken to be related to these sources through some unknown function. Furthermore, the (unknown) number of underlying latent sources may be less than the number of observations. Recent developments in independent component analysis (ICA) have shown that, in the case where the unknown function linking sources to observations is linear, such data decomposition may be achieved in a mathematically elegant manner. In this paper, we extend the general ICA paradigm to include a very flexible source model, prior constraints and conditioning on sets of intermediate variables so that ICA forms one part of a hierarchical system. We show that such an approach allows for efficient discovery of hidden representation in data and for unsupervised data partitioning.  相似文献   
998.
毕宝臣  史江涛 《铁合金》2003,34(5):41-43
对炉眼烧损原因进行了分析,矿热炉通过使用开堵眼机,减少了炉眼烧损,解决了跑眼频繁、出铁口使用寿命短的问题,并取得了一定的经济效益。  相似文献   
999.
电控柴油机以其节能、环保、易于控制等特点。获得了广泛的应用。为了更好地了解该项新产品,使其尽早在石油机械上推广使用。提升中国石油机械的品质,文章对电控柴油机的特点、结构及应用前景进行了讨论。  相似文献   
1000.
Cu-Cr合金高温氧化行为分析   总被引:3,自引:0,他引:3  
该文用热分析天平,结合金相、X射线衍射(XRD)、扫描电镜(SEM)和能谱(EXD)研究了Cu—Cr合金在不同温度下的氧化行为。结果表明,Cu—Cr合金在700℃-900℃氧化符合抛物线规律,其最外层氧化膜为CuO,内层为Cu2O和Cr2O3,铬有助于提高合金的抗氧化能力。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号